Abstract
From the standpoint of saving water in home laundry, the effect of soiling on white cotton cloths was investigated by using washing water to which bath liquid containing pigments had been added. The used bath liquid contained ca. 93% inorganic salt (NaHCO3, Na2SO4, etc.) and a few kinds of pigments (acid dye), and its instructed concentration was 30 g/200l (0.015%). The soiling experiment was carried out using a washing machine and an incubator. The degree of soiling was measured by Hunter's color difference (ΔE) using a color difference meter. Soiling by 6 kinds of pigments on white cotton cloths decreased in the order of red No. 230 (1) >orange No. 205>blue No.2>yellow No. 5>red No. 106>green No. 204, at NaHCO3 0.1% solution. As a result of repeated laundering using the water containing bath liquid, the degree of soiling on cotton cloths increased, although pigment concentration was very low (0.20-0.45 ppm) in 0.015% bath liquid. Soiling of pigment increased remarkably when inorganic salts were added in comparison with surfactant, and it decreased in the order of Na2SO4>Na2CO3>NaHCO3. Therefore, it was suggested that the Na2SO4 component in laundry detergent solution promotes soiling by pigments when the concentration is higher than that of bath liquid salts.
